There is compelling evidence to suggest that there is a strong correlation between the sharply increasing levels of atmospheric CO2 with a commensurate increase in global surface temperatures. This effect is commonly known as Global Warming. Of the various sources of the CO2 emissions, there are a vast number of small, widely distributed emitters that are impractical to mitigate at the source. Additionally, large scale emitters such as hydrocarbon-fueled power plants are not fully protected from exhausting CO2 into the atmosphere. Combined, these major sources, as well as others, have led to the creation of a sharply increasing rate of atmospheric CO2 concentration. Until all emitters are corrected at their source, other technologies are required to capture the increasing, albeit relatively low, background levels of atmospheric CO2. Efforts are underway to augment existing emissions reducing technologies as well as the development of new and novel techniques for the direct capture of ambient CO2. These efforts require methodologies to manage the resulting concentrated waste streams of CO2 in such a manner as to prevent its reintroduction to the atmosphere.
The production of CO2 occurs in a variety of industrial applications such as the generation of electricity power plants from coal and in the use of hydrocarbons that are typically the main components of fuels that are combusted in combustion devices, such as engines. Exhaust gas discharged from such combustion devices contains CO2 gas, which at present is simply released to the atmosphere. However, as greenhouse gas concerns mount, CO2 emissions from all sources will have to be curtailed. For mobile sources the best option is likely to be the collection of CO2 directly from the air rather than from the mobile combustion device in a car or an airplane. The advantage of removing CO2 from air is that it eliminates the need for storing CO2 on the mobile device.
Extracting carbon dioxide (CO2) from ambient air would make it possible to use carbon-based fuels and deal with the associated greenhouse gas emissions after the fact. Since CO2 is neither poisonous nor harmful in parts per million quantities, but creates environmental problems simply by accumulating in the atmosphere, it is possible to remove CO2 from air in order to compensate for equally sized emissions elsewhere and at different times.
The art has proposed various schemes for removal of CO2 from combustion exhaust gases or directly from the air by subjecting the gases or air to a pressure swing or a thermal swing using a CO2 adsorbent. These processes use pressure or temperature changes, respectively, to change the state of the sorbent material, whereby to release the CO2. Different sorbent materials are disclosed, including zeolites, amines, and activated alumina. See, for example, U.S. Pat. No. 4,711,645; U.S. Pat. No. 5,318,758; U.S. Pat. No. 5,914,455; U.S. Pat. No. 5,980,611; U.S. Pat. No. 6,117,404; and co-pending U.S. application Ser. No. 11/683,824, the contents of which are incorporated herein by reference.
None of these references, however, provides a particularly efficient process for the removal of CO2, primarily due to the amount of energy expended in CO2 recovery and sorbent regeneration.